Pinmux with device tree

[Stephen Warren]

Grant Likely wrote at Thursday, May 19, 2011 11:10 AM
> On Thu, May 19, 2011 at 07:30:52PM +0800, Haojian Zhuang wrote:
> > On Thu, May 19, 2011 at 3:33 AM, Mitch Bradley <wmb at firmworks.com> wrote:
> > > On 5/18/2011 6:34 AM, Simon Glass wrote:
> > >>
> > >> Hi,
> > >>
> > >> I see a new pinmux system in the LKML. Has anyone looked at how to
> > >> represent pinmux settings in the device tree?
> > >>
> > >> On a related topic, the examples that are used for GPIOs assume a
> > >> flags word which describes things like pull-ups, direction, etc. This
> > >> seems pretty cumbersome and gets worse with pinmuxes. People editing
> > >> the device trees want to see symbolic information rather than a coded
> > >> number, a bit like a #define. I can see this can be done with strings
> > >> but this is inefficient in time and space, and is error-prone.  Is
> > >> there support for this in device trees that I have missed?
> 
> Why is it error prone?  It is probably less error prone than using
> magic integer values.  :-)

I think that comment was saying that if the FDT itself contains the strings,
if there were a typo, it'd only be detected at run-time (well, admittedly
just like a typo in a number).

However, if the DT compiler implemented something like the pre-processor,
any typos in define usage would be detected at compile time due to referencing
a non-existing define/variable, which is less error-prone.

I must admit, when I first saw DT source files, my first though was to run
CPP on them (or similar token->integer replacement utility, which also
supported bitwise math e.g. for the GPIO flags stuff), and then pass the
result to dtc, so that I could work with names instead of numbers.

--
nvpublic